1. Field of the Invention
The present invention relates to surface emitting laser and surface emitting laser array, and in particular, to the structure of surface emitting laser which includes phase adjusting layer and electric current constricting layer.
2. Description of the Related Art
As the name suggests, in VCSEL (Vertical Cavity Surface Emitting Laser, hereinafter simply referred to as “surface emitting laser”) elements, the direction in which light resonates is perpendicular to the substrate surface and they are brought to attention in various applications like optical interconnection, a light source for communication, and sensors etc. This is because, as compared to the conventional edge emitting semiconductor laser, two-dimensional array of the laser element can be created more easily, the testing can be done at wafer level as cleavage is not required for creating the mirror, oscillation can be done with an extremely small threshold due to the active layer volume being very small, and the power consumption is small.
In the surface emitting laser having a relatively long oscillation wavelength of 1100 to 1550 nm bandwidth, it is challenging to improve the characteristics like performing a high-power operation at a high temperature while maintaining the electric current with a low threshold in a single mode. This especially is challenging in the surface emitting laser having an oscillation wavelength of 1300 to 1550 nm bandwidth.
A structure that causes reduction in losses in the intra-cavity structure has been proposed in the U.S. Pat. No. 6,618,414 (hereinafter referred to as “the patent reference”). In the structure that is proposed, a phase adjusting layer (referred to as “spacer layer” in the patent reference) has been created between the contact layer comprising a semiconductor layer and a dielectric DBR (Distributed Bragg Reflector) mirror that configures the upper reflecting mirror forming one side of a resonator. By using this structure, nodes of standing wave of light is adjusted with the position of the spacer layer, and light absorption at the heavily doped contact layer is suppressed to the minimum, and thereby, a high-power operation at a high temperature while maintaining the electric current with a low threshold is achieved.
In the patent reference in which the surface emitting laser structure having such dielectric DBR mirror and phase adjusting layer is proposed, although high-power operation is achieved at a high temperature while maintaining the electric current with a low threshold, investigation is insufficient regarding the single mode characteristics, and there is no description in particular regarding the relation to be maintained between the phase adjusting layer and the electric current constricting layer to be created. In other words, conventionally, there was no knowledge regarding the relation to be maintained between the phase adjusting layer and the electric current constricting layer with respect to the single mode characteristics, in the structure in surface emitting lasers described in the patent reference. The present inventors realized that the relation between both these layers are important in determining the single mode characteristics and we were successful in manufacturing a surface emitting laser having practical oscillation characteristics.